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Production forecasting decline curve analysis: Difference between revisions
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Production forecasting decline curve analysis (view source)
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, 26 November 2018The paper by Roland Horne had a typo in the SPE paper number.
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*Arps 1945 and 1956. | *Arps 1945 and 1956. | ||
*Brons 1963 and Fetkovitch 1983 applied constant pressure solution to | *Brons 1963 and Fetkovitch 1983 applied constant pressure solution to diffusivity equation and demonstrated that exponential decline curve actually reflects single phase, incompressible fluid production from a closed reservoir. DCA is more than a empirical curve fit. | ||
*Fetkovitch 1980 and 1983 developed set of type curves to enhance application of DCA. | *Fetkovitch 1980 and 1983 developed set of type curves to enhance application of DCA. | ||
*Doublet and Blasingame 1995 developed theoretical basis for combining transient and boundary dominated flow for the pressure transient solution to the diffusivity equation. | *Doublet and Blasingame 1995 developed theoretical basis for combining transient and boundary dominated flow for the pressure transient solution to the diffusivity equation. | ||
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Clearly all wells do not exhibit exponential behavior during depletion. In many cases a more gradual hyperbolic decline is observed where rate time performance is better than estimated from exponential solutions implying that hyperbolic decline results from natural and artificial driving energies that slow down pressure depletion. Hyperbolic decline is observed when reservoir drive mechanism is solution gas cap drive, gas cap expansion or water drive. It is also possible where natural drive is supplemented by injection of water gas. The type of decline and its characteristic shape is a major feature of DCA. We shall be talking more about this as we go further. The various types of declines experienced by a well are documented in the '''Fig 1 and Fig 2'''. | Clearly all wells do not exhibit exponential behavior during depletion. In many cases a more gradual hyperbolic decline is observed where rate time performance is better than estimated from exponential solutions implying that hyperbolic decline results from natural and artificial driving energies that slow down pressure depletion. Hyperbolic decline is observed when reservoir drive mechanism is solution gas cap drive, gas cap expansion or water drive. It is also possible where natural drive is supplemented by injection of water gas. The type of decline and its characteristic shape is a major feature of DCA. We shall be talking more about this as we go further. The various types of declines experienced by a well are documented in the '''Fig 1 '''and'''Fig 2'''. | ||
INSERT FIGURE 1 q vs. Time showing various types of declines on Cartesian plot. (b value for hyperbolic curve =0.5) | INSERT FIGURE 1 q vs. Time showing various types of declines on Cartesian plot. (b value for hyperbolic curve =0.5)<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
INSERT FIGURE 2 Log q vs. Time showing various types of declines on Semilog plot. (b value for hyperbolic curve =0.5). Note change in shapes of curves. | INSERT FIGURE 2 Log q vs. Time showing various types of declines on Semilog plot. (b value for hyperbolic curve =0.5). Note change in shapes of curves.<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
Observe the change in Shapes of curve from Cartesian to logarithmic; this is very helpful in identification of type of decline. | Observe the change in Shapes of curve from Cartesian to logarithmic; this is very helpful in identification of type of decline. | ||
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INSERT FIGURE 3 Rate verses Time and Rate verses Cum Oil | INSERT FIGURE 3 Rate verses Time and Rate verses Cum Oil<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
=== Exponential Decline === | === Exponential Decline === | ||
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Applies to a well producing at constant bottom hole pressure. | Applies to a well producing at constant bottom hole pressure. | ||
INSERT FIGURE 4 Rate vs. Time – Exponential Decline | INSERT FIGURE 4 Rate vs. Time – Exponential Decline<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
INSERT FIGURE 5 Rate vs. Cum Oil – Exponential Decline | INSERT FIGURE 5 Rate vs. Cum Oil – Exponential Decline<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
Reservoir types with exponential declines<ref>Fetkovich, M. J., Fetkovich, E. J., & Fetkovich, M. D. | Reservoir types with exponential declines<ref>Fetkovich, M. J., Fetkovich, E. J., & Fetkovich, M. D. 1996. Useful Concepts for Decline Curve Forecasting, Reserve Estimation, and Analysis. Society of Petroleum Engineers. http://dx.doi.org/10.2118/28628-PA</ref>: | ||
*Oil reservoirs | *Oil reservoirs | ||
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*Thus an ‘effective’ decline of 10 % per year is equivalent to a nominal decline of 10.54% per year and vice versa | *Thus an ‘effective’ decline of 10 % per year is equivalent to a nominal decline of 10.54% per year and vice versa | ||
INSERT Figure 6 Effective and Nominal Decline, Shape and Relationship | INSERT Figure 6 Effective and Nominal Decline, Shape and Relationship<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
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*Forecast of ultimate recovery should give a reasonable recovery factor based on estimated volumes of hydrocarbons in place. | *Forecast of ultimate recovery should give a reasonable recovery factor based on estimated volumes of hydrocarbons in place. | ||
INSERT Figure 7 Application of minimum decline concept | INSERT Figure 7 Application of minimum decline concept<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
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==Determining the type of decline== | == Determining the type of decline == | ||
Based on what has been covered so far, the engineer performing a DCA analysis needs to be aware of the following: | Based on what has been covered so far, the engineer performing a DCA analysis needs to be aware of the following: | ||
# The most representative period in history that will also represent future. | |||
# The decline trend during that period. | #The most representative period in history that will also represent future. | ||
# The start point(rate) of forecast . | #The decline trend during that period. | ||
# The constraints under which the forecast needs to be made. | #The start point(rate) of forecast . | ||
#The constraints under which the forecast needs to be made. | |||
However one more factor, also extremely important at this stage is to determine type of decline. Since the signature of shape may not be apparent on a log q vs. time (most used plot), literature provides many ways was to look at the same data, combine this information with other knowledge about the fields before we make our conclusions. . | However one more factor, also extremely important at this stage is to determine type of decline. Since the signature of shape may not be apparent on a log q vs. time (most used plot), literature provides many ways was to look at the same data, combine this information with other knowledge about the fields before we make our conclusions. . | ||
As shown in Figures 8 to 11 Shapes of curves for the same data plotted in different ways helps determine the type of declines. | As shown in Figures 8 to 11 Shapes of curves for the same data plotted in different ways helps determine the type of declines.<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
INSERT Figure 8: Rate vs. Cum Oil | INSERT Figure 8: Rate vs. Cum Oil - Cartesian Axes – Exponential decline is a straight line<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
INSERT Figure 9: Log Rate vs. Cum Oil | INSERT Figure 9: Log Rate vs. Cum Oil - Semilog – Harmonic decline is a straight line<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
INSERT Figure 10: Rate vs. Time | INSERT Figure 10: Rate vs. Time - Cartesian Axes<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
INSERT Figure 11: Log Rate vs. Time | INSERT Figure 11: Log Rate vs. Time - Semilog – Exponential decline is a straight line<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
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==Decline curves for reserve estimates== | == Decline curves for reserve estimates == | ||
A major use of decline curve analysis is made in estimation of reserves. Even for the assets where history matched simulation models are available, a cross check with DCA is normally made to give increased confidence in numbers. | A major use of decline curve analysis is made in estimation of reserves. Even for the assets where history matched simulation models are available, a cross check with DCA is normally made to give increased confidence in numbers. | ||
An in-depth description of application of DCA to reserves estimation is outside the purview of this guideline, however some typical situation and their treatment are discussed in section II of this chapter. | The fact that DCA does not have a theoretical basis is an asset here since financial institutions are more acceptable to DCA estimates than other more technical methodologies. A major difference when applying DCA for estimation of reserves arises understandably due the very nature of definitions of reserves and financial implications associated with the process. The ultimate recovery numbers become more important than the profiles. Application of constraints in the production system, operating costs, capital costs and well behavior itself all need to be put into right perspective to come up with reliable estimations. | ||
An in-depth description of application of DCA to reserves estimation is outside the purview of this guideline, however some typical situation and their treatment are discussed in section II of this chapter. | |||
While everything else remains same, estimation of reserves does come up with several typical situations to which there are no ready answers. Some of these situations are listed out below for reference. The solutions to these problems could vary from engineer to engineer or organization to organization. Some of the best practices have however been compiled and can be found in | While everything else remains same, estimation of reserves does come up with several typical situations to which there are no ready answers. Some of these situations are listed out below for reference. The solutions to these problems could vary from engineer to engineer or organization to organization. Some of the best practices have however been compiled and can be found in [http://petrowiki.org/Production_forecasting_principles_and_definition production forecasting principles and definition]. | ||
* What should be the start point of the forecast if rate changes significantly in last or last few months. | *What should be the start point of the forecast if rate changes significantly in last or last few months. | ||
* How to get a P10, P50, P90 estimate using decline curves. | *How to get a P10, P50, P90 estimate using decline curves. | ||
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===Using decline curves=== | === Using decline curves === | ||
Decline analysis and forecasts generated based on such analysis (whether production profiles or reserves) should be fundamentally grounded in good understanding of the factors that control this behavior. ‘No One size fits all ‘ this principal applies truly and universally when it comes to application of DCA. Specifically always arbitrarily using an exponential decline approach for water drive, solution gas drive and gravity drainage systems is neither technically not empirically justified. | |||
Decline analysis and forecasts generated based on such analysis (whether production profiles or reserves) should be fundamentally grounded in good understanding of the factors that control this behavior. ‘No One size fits all ‘ this principal applies truly and universally when it comes to application of DCA. Specifically always arbitrarily using an exponential decline approach for water drive, solution gas drive and gravity drainage systems is neither technically not empirically justified. | |||
=== DCA in waterflood and ratio plots === | |||
Field cases as well as analytical / simulation generally support hyperbolic/harmonic decline for late stage waterflood behavior meaning that value of b lies 0<b<1. This is not to say that exponential decline or super harmonic decline will/may not occur in waterflood reservoirs. However whenever such phenomenon is observed, usually non reservoir factors are at play. | Field cases as well as analytical / simulation generally support hyperbolic/harmonic decline for late stage waterflood behavior meaning that value of b lies 0<b<1. This is not to say that exponential decline or super harmonic decline will/may not occur in waterflood reservoirs. However whenever such phenomenon is observed, usually non reservoir factors are at play. | ||
In order to estimate future waterflood performance we need to examine what is controlling the oil decline rate. After substantial water breakthrough, the rate is usually controlled by | In order to estimate future waterflood performance we need to examine what is controlling the oil decline rate. After substantial water breakthrough, the rate is usually controlled by | ||
* Relative permeability | |||
* Changing volumetric sweep | *Relative permeability | ||
* Water handling constraints | *Changing volumetric sweep | ||
* Fluid rates handling constraints | *Water handling constraints | ||
* Permeability injectivity in near wellbore regions | *Fluid rates handling constraints | ||
* Well positions. | *Permeability injectivity in near wellbore regions | ||
*Well positions. | |||
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DCA as applied to Waterflood cases needs to consider the following criteria ( Reservoir Management for Waterfloods, R O Baker, JCPT, Jan 1998): | DCA as applied to Waterflood cases needs to consider the following criteria ( Reservoir Management for Waterfloods, R O Baker, JCPT, Jan 1998): | ||
* Watercut is greater than 50% | *Watercut is greater than 50% | ||
* Voidage replacement ration is close to or equal to 1 | *Voidage replacement ration is close to or equal to 1 | ||
* Well count is relatively stable | *Well count is relatively stable | ||
* Injection rates and fluid production rates remain fairly stable | *Injection rates and fluid production rates remain fairly stable | ||
* Reservoir pressure remains relatively constant | *Reservoir pressure remains relatively constant | ||
* The volume of water injected should be greater than 25% of the hydrocarbon pore volume. | *The volume of water injected should be greater than 25% of the hydrocarbon pore volume. | ||
RF vs. HCPVI, Log (WOR) vs. | RF vs. HCPVI, Log (WOR) vs. Np, Log (Qo+Qw) vs. Np and Masoner plots should be also used in waterflood cases in addition to conventional methods mentioned earlier to ensure estimation of incremental recoveries due to Waterflood and/or impact on recovery due to constraints in the system. As a special case, Roland Horne..et al (SPE 83470) have proposed techniques to apply DCA on naturally fractured reservoirs that have been developed using waterflooding. | ||
As a special case, Roland Horne..et al (SPE | |||
===Ratio plots=== | === Ratio plots === | ||
INSERT Figure 12: Ratio plot WOR vs. Cum Oil – Characteristic Shapes | Reservoirs producing with high watercut, high GOR need to be analyzed using ratio plots in conjunction with conventional plots to ensure there is no overestimation of volumes based on rate plots only. (Log WOR vs. Np, Log GOR vs. Np, Watercut vs. Np). Care needs to be taken to understand the minimum criteria for application of these plots. For example Log WOR vs. Cum Oil should only be used if WOR is equal to or higher than 1 ( water cut is equal to higher than 50%). | ||
INSERT Figure 12: Ratio plot WOR vs. Cum Oil – Characteristic Shapes<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | |||
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==Advanced Work== | == Advanced Work == | ||
The DCA technique is most reliable for wells producing at high drawdown against relatively constant flowing pressures, such that the production rate decline mirrors the decline in reservoir pressure. Because of this tie to reservoir pressure, most practitioners restricted its use to the boundary-dominated flow period. However, development of tight and unconventional reservoirs has extended its usage in the transient flow period, necessitating the development of alternative techniques that generally attempt to match the transient and boundary-dominated flow periods using separate parameters. | |||
The decline curve treatment offered by Arps was largely applicable to boundary dominated flow (depletion period), whereas Fetkovich focused on the early period of production i.e. transient flow and came up with set of type curves | The DCA technique is most reliable for wells producing at high drawdown against relatively constant flowing pressures, such that the production rate decline mirrors the decline in reservoir pressure. Because of this tie to reservoir pressure, most practitioners restricted its use to the boundary-dominated flow period. However, development of tight and unconventional reservoirs has extended its usage in the transient flow period, necessitating the development of alternative techniques that generally attempt to match the transient and boundary-dominated flow periods using separate parameters. The decline curve treatment offered by Arps was largely applicable to boundary dominated flow (depletion period), whereas Fetkovich focused on the early period of production i.e. transient flow and came up with set of type curves that could be combined with Arps empirical decline curve equation. | ||
Accordingly, the Fetkovich type curves are made up of two regions which have been blended to be continuous and thereby encompass the whole production life from early time (transient flow) to late time (boundary dominated flow) | Accordingly, the Fetkovich type curves are made up of two regions which have been blended to be continuous and thereby encompass the whole production life from early time (transient flow) to late time (boundary dominated flow) | ||
The right hand side of Fetkovich type curves is identical to Arps type curve as shown below: | The right hand side of Fetkovich type curves is identical to Arps type curve as shown below: | ||
INSERT Figure 13: Arp's Dimensionless curve for empirical Rate-time decline Equations | INSERT Figure 13: Arp's Dimensionless curve for empirical Rate-time decline Equations<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
The left hand side of Fetkovich type curves are derived from the analytical solution to the flow of a well in the center of a finite circular reservoir producing at a constant wellbore flowing pressure. Fetkovich was able to demonstrate that for all sizes of reservoirs, when transient flow ended, the boundary dominated flow could be represented by an exponential decline as shown below: | The left hand side of Fetkovich type curves are derived from the analytical solution to the flow of a well in the center of a finite circular reservoir producing at a constant wellbore flowing pressure. Fetkovich was able to demonstrate that for all sizes of reservoirs, when transient flow ended, the boundary dominated flow could be represented by an exponential decline as shown below: | ||
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INSERT Figure 14: Fetkovich Rate Decline Curves | INSERT Figure 14: Fetkovich Rate Decline Curves<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
Combining the Fetkovich transient type curves with Arps decline curves and blending them where the two sets of curves meet, results in Fetkovich Decline Type Curves as shown below: | Combining the Fetkovich transient type curves with Arps decline curves and blending them where the two sets of curves meet, results in Fetkovich Decline Type Curves as shown below: | ||
Important : Fetkovich noted that sometimes the value of b as determined using Arps decline curves was greater than 1( expected to be between 0 and 1). He explained that this could happen if the data being analyzed was still in transient condition and has not reached boundary dominated flow. | Important: Fetkovich noted that sometimes the value of b as determined using Arps decline curves was greater than 1( expected to be between 0 and 1). He explained that this could happen if the data being analyzed was still in transient condition and has not reached boundary dominated flow. | ||
INSERT Figure 15 | INSERT Figure 15: Fetkovich Decline type curves<span style="color: rgb(34, 34, 34); font-family: sans-serif; font-size: 12.8px; line-height: 19.2px;"> (Pending permission approval)</span> | ||
Methods specifically developed for unconventional resources are covered in detail in | Methods specifically developed for unconventional resources are covered in detail in [http://petrowiki.org/Types_of_decline_analysis_in_production_forecasting Types of decline analysis in production forecasting]. | ||
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[http://petrowiki.org/Production_forecasting_glossary Production forecasting glossary] | [http://petrowiki.org/Production_forecasting_glossary Production forecasting glossary] | ||
[http://petrowiki.org/ | [http://petrowiki.org/Aggregation_of_forecasts Aggregation of forecasts] | ||
[http://petrowiki.org/Challenging_the_current_barriers_to_forecast_improvement Challenging the current barriers to forecast improvement] | |||
[http://petrowiki.org/Commercial_and_economic_assumptions_in_production_forecasting Commercial and economic assumptions in production forecasting] | |||
[http://petrowiki.org/Controllable_verses_non_controllable_forecast_factors Controllable verses non controllable forecast factors] | |||
[http://petrowiki.org/Discounting_and_risking_in_production_forecasting Discounting and risking in production forecasting] | |||
[http://petrowiki.org/Documentation_and_reporting_in_production_forecasting Documentation and reporting in production forecasting] | |||
[http://petrowiki.org/Empirical_methods_in_production_forecasting Empirical methods in production forecasting] | |||
[http://petrowiki.org/Establishing_input_for_production_forecasting Establishing input for production forecasting] | |||
[http://petrowiki.org/Integrated_asset_modelling_in_production_forecasting Integrated asset modelling in production forecasting] | |||
[http://petrowiki.org/Long_term_verses_short_term_production_forecast Long term verses short term production forecast] | |||
[http://petrowiki.org/Look_backs_and_forecast_verification Look backs and forecast verification] | |||
[http://petrowiki.org/Material_balance_models_in_production_forecasting Material balance models in production forecasting] | |||
[http://petrowiki.org/Probabilistic_verses_deterministic_in_production_forecasting Probabilistic verses deterministic in production forecasting] | |||
[http://petrowiki.org/Production_forecasting_activity_scheduling Production forecasting activity scheduling] | |||
[http://petrowiki.org/Production_forecasting_analog_methods Production forecasting analog methods] | |||
[http://petrowiki.org/Production_forecasting_building_blocks Production forecasting building blocks] | |||
[http://petrowiki.org/Production_forecasting_decline_curve_analysis Production forecasting decline curve analysis] | |||
[http://petrowiki.org/Production_forecasting_expectations Production forecasting expectations] | |||
[http://petrowiki.org/Production_forecasting_flowchart Production forecasting flowchart] | |||
[http://petrowiki.org/Production_forecasting_frequently_asked_questions_and_examples Production forecasting frequently asked questions and examples] | |||
[http://petrowiki.org/Production_forecasting_in_the_financial_markets Production forecasting in the financial markets] | |||
[http://petrowiki.org/Production_forecasting_principles_and_definition Production forecasting principles and definition] | |||
[http://petrowiki.org/Production_forecasting_purpose Production forecasting purpose] | |||
[http://petrowiki.org/Production_forecasting_system_constraints Production forecasting system constraints] | |||
[http://petrowiki.org/Quality_assurance_in_forecast Quality assurance in forecast] | |||
[http://petrowiki.org/Reservoir_simulation_models_in_production_forecasting Reservoir simulation models in production forecasting] | |||
[http://petrowiki.org/Types_of_decline_analysis_in_production_forecasting Types of decline analysis in production forecasting] | |||
[http://petrowiki.org/ | [http://petrowiki.org/Uncertainty_analysis_in_creating_production_forecast Uncertainty analysis in creating production forecast] | ||
[http://petrowiki.org/ | [http://petrowiki.org/Uncertainty_range_in_production_forecasting Uncertainty range in production forecasting] | ||
[http://petrowiki.org/ | [http://petrowiki.org/Using_multiple_methodologies_in_production_forecasting Using multiple methodologies in production forecasting] | ||
[[#Top|Back to top]] | [[#Top|Back to top]] | ||
== Category == | == Category == | ||
[[Category:5.6 Formation evaluation and management]] [[Category:5.6.9 Production forecasting]] [[Category: | [[Category:5.6 Formation evaluation and management]] [[Category:5.6.9 Production forecasting]] [[Category:GIWS-PF]] [[Category:Chapter 7]] [[Category:DW]] [[Category:DW Complete]] [[Category:DW All Pages]] | ||